merge.rb

right = { 'alphabet' => ['r', 'i', 'g', 'h', 't'] }
left  = { 'alphabet' => ['l', 'e', 'f', 't'] }

right.merge(left)
#=> {"alphabet"=>["l", "e", "f", "t"]}
#=> be overwritten

right.merge(left){|key, old, new| old + new}
#=> {"alphabet"=>["r", "i", "g", "h", "t", "l", "e", "f", "t"]}

key = 'alphabet'
new_hash[key] = right[key] + left[key]

Hmm.......